Open Access

Delivered dose of renal replacement therapy and mortality in critically ill patients with acute kidney injury

  • Sergio Vesconi1,
  • Dinna N Cruz2Email author,
  • Roberto Fumagalli3,
  • Detlef Kindgen-Milles4,
  • Gianpaola Monti1,
  • Anibal Marinho5,
  • Filippo Mariano6,
  • Marco Formica7,
  • Mariano Marchesi8,
  • René Robert9,
  • Sergio Livigni10,
  • Claudio Ronco2 and
  • the DOse REsponse Multicentre International collaborative Initiative (DO-RE-MI Study Group)
Contributed equally
Critical Care200913:R57

https://doi.org/10.1186/cc7784

Received: 24 November 2008

Accepted: 15 April 2009

Published: 15 April 2009

Abstract

Introduction

The optimal dialysis dose for the treatment of acute kidney injury (AKI) is controversial. We sought to evaluate the relationship between renal replacement therapy (RRT) dose and outcome.

Methods

We performed a prospective multicentre observational study in 30 intensive care units (ICUs) in eight countries from June 2005 to December 2007. Delivered RRT dose was calculated in patients treated exclusively with either continuous RRT (CRRT) or intermittent RRT (IRRT) during their ICU stay. Dose was categorised into more-intensive (CRRT ≥ 35 ml/kg/hour, IRRT ≥ 6 sessions/week) or less-intensive (CRRT < 35 ml/kg/hour, IRRT < 6 sessions/week). The main outcome measures were ICU mortality, ICU length of stay and duration of mechanical ventilation.

Results

Of 15,200 critically ill patients admitted during the study period, 553 AKI patients were treated with RRT, including 338 who received CRRT only and 87 who received IRRT only. For CRRT, the median delivered dose was 27.1 ml/kg/hour (interquartile range (IQR) = 22.1 to 33.9). For IRRT, the median dose was 7 sessions/week (IQR = 5 to 7). Only 22% of CRRT patients and 64% of IRRT patients received a more-intensive dose. Crude ICU mortality among CRRT patients were 60.8% vs. 52.5% (more-intensive vs. less-intensive groups, respectively). In IRRT, this was 23.6 vs. 19.4%, respectively. On multivariable analysis, there was no significant association between RRT dose and ICU mortality (Odds ratio (OR) more-intensive vs. less-intensive: CRRT OR = 1.21, 95% confidence interval (CI) = 0.66 to 2.21; IRRT OR = 1.50, 95% CI = 0.48 to 4.67). Among survivors, shorter ICU stay and duration of mechanical ventilation were observed in the more-intensive RRT groups (more-intensive vs. less-intensive for all: CRRT (median): 15 (IQR = 8 to 26) vs. 19.5 (IQR = 12 to 33.5) ICU days, P = 0.063; 7 (IQR = 4 to 17) vs. 14 (IQR = 5 to 24) ventilation days, P = 0.031; IRRT: 8 (IQR = 5.5 to 14) vs. 18 (IQR = 13 to 35) ICU days, P = 0.008; 2.5 (IQR = 0 to 10) vs. 12 (IQR = 3 to 24) ventilation days, P = 0.026).

Conclusions

After adjustment for multiple variables, these data provide no evidence for a survival benefit afforded by higher dose RRT. However, more-intensive RRT was associated with a favourable effect on ICU stay and duration of mechanical ventilation among survivors. This result warrants further exploration.

Trial Registration

Cochrane Renal Group (CRG110600093).

Introduction

Acute kidney injury (AKI) requiring renal replacement therapy (RRT) occurs in 5 to 6% of critically ill patients and is associated with high mortality and significant health resource utilization [13]. Controversy exists as to what constitutes optimal RRT in this setting. There are several modifiable factors in the delivery of RRT which may potentially influence patient outcome, including RRT modality (continuous or intermittent), solute removal mechanisms (convection, diffusion, adsorption or combination), timing of initiation and dose of treatment. The relationship between patient outcome and treatment dose was first introduced in a landmark study where patients randomised to post-dilution continuous veno-venous haemofiltration (CVVH) at a dose of 35 ml/kg/hour or above had improved survival compared with those randomised to 20 ml/kg/hour [4]. Since then, this issue has been explored in other studies with conflicting results [59]. The Acute Dialysis Quality Initiative recommends a higher dose in the absence of definitive data, particularly in septic patients [10, 11]. However, practice surveys suggest that this threshold dose has not been widely adopted into current intensive care units (ICU) practice [12, 13].

We performed a prospective European multicentre observational cohort study to evaluate the prescription and actual-delivered RRT dose in ICUs and its relationship with patient outcome, such as mortality and duration of mechanical ventilation and ICU stay. Our hypothesis was that a higher RRT dose would be associated with better patient outcomes.

Materials and methods

This study was conducted from June 2005 to December 2007 in 757 patients enrolled in 30 ICUs in eight countries. The protocol was approved by the institutional review boards of the five Steering Committee members. Written informed consent was obtained from patients or next of kin when required by a centre's review board. The design of the study was published in 2005 [14], and registered in the Cochrane Renal Group (CRG110600093).

Study population

All incident patients aged 12 years or older treated with RRT in the ICU were eligible for inclusion in the study. Patients with pre-existing chronic kidney disease stage 5 were excluded from analysis. Patients were categorised by treatment modality (Figure 1). AKI was defined using the Risk-Injury-Failure-Loss-End stage renal disease (RIFLE) classification [15].
Figure 1

Profile of study population. Calculation of RRT dose was performed on patients who were treated exclusively on one RRT schedule (CRRT only or IRRT only). Forty six patients were treated with mixed RRT schedules (CRRT + CPFA, n = 10; CRRT + IRRT, n = 36; see text for explanation). AKI = acute kidney injury; CKD = chronic kidney disease; CPFA = coupled plasmafiltration adsorption; CRRT = continuous renal replacement therapy; ESRD = end-stage renal disease; ICU = intensive care unit; IRRT = intermittent renal replacement therapy.

Data collection

Data from enrolled patients were entered into electronic case report forms resident on a password-protected web server [16]. Individual centres only had access to data relevant to their patients. Multiple data elements were collected for each patient [14]. Periodic audits were performed to establish the integrity of data capture and transfer into the database, as well as data accuracy.

Calculation of delivered and prescribed RRT dose

Although several mathematical models have been developed to correlate the RRT dose given on different schedules (i.e. intermittent (IRRT) and continuous (CRRT)), none of these models have been rigorously validated in clinical practice [1719]. We therefore chose to express the dose of CRRT and IRRT based on current clinical practice rather than a theoretical equivalent expression of dose [see Additional data file 1]. CVVH, continuous veno-venous haemodialysis (CVVHD), continuous veno-venous haemodiafiltration (CVVHDF) and high volume hemofiltration (HVHF) were analysed together as CRRT; dose was calculated using total effluent (the sum of the dialysate and ultrafiltrate) with correction for percentage predilution, and expressed as ml/kg/hour [20]. IRRT dose was expressed as the number of sessions per week [9]. Patients were categorised into those receiving more-intensive (CRRT ≥ 35 ml/kg/hour, IRRT ≥ 6 sessions/week) [9] or less-intensive (CRRT < 35 ml/kg/hour, IRRT < 6 sessions/week). Distribution of CRRT and IRRT dose are shown in Figure 1 in Additional data file 2. RRT and concurrent ICU care were instituted and prescribed at discretion of the treating physician.

End points

ICU mortality was the primary outcome. The secondary outcomes were ICU length of stay and duration of mechanical ventilation.

Statistical analyses

Continuous variables are expressed as mean ± standard deviation or median (interquartile range) and compared between any two groups using t-test or the Mann Whitney U test, and among three groups using analysis of variance (general linear models with adjustment for multiple comparisons) or the Kruskal-Wallis test, where appropriate. Categorical variables are expressed as proportions and compared with the Mantel-Haenszel chi-squares test or Fisher's exact test.

For the analysis of RRT dose versus outcome, CRRT and IRRT patients were analysed separately because of well-recognised differences between these populations in observational studies [21, 22]. Exploratory univariate analysis for several variables was performed to identify possible risk (or protective) factors associated with ICU mortality. Multivariable logistic regression analysis was then conducted to test the relationship between RRT dose and ICU mortality, adjusted for confounding factors.

Based on the results of the univariate analysis, the covariates included in the CRRT model were sex, age (10-year increments), sequential organ failure assessment (SOFA) and serum creatinine at CRRT initiation and CRRT downtime (hours); for IRRT the covariates included were age (10-years increments), sex and RIFLE class at IRRT initiation. In addition to adjusting for significant covariates, residual confounding and selection effects were addressed using propensity scores. We generated a propensity score using multivariable logistic regression with more-intensive RRT dose as the dependent variable, as previously described [22, 23]. Variables included in the propensity score were gender, weight, SOFA score and serum creatinine at RRT initiation. We fitted models for ICU mortality only adjusted for covariates and a combination of covariates plus the propensity score. We assessed for collinearity between variables using tolerance and variance inflation factors; there was no significant collinearity detected. The model's goodness of fit was tested with the Hosmer-Lemeshow statistic.

As sensitivity analyses, RRT dose was evaluated as both continuous variables and categorical variables. As continuous variable for CRRT, we used the actual value or as increments of 10 ml/kg/hour; for IRRT, we used number of IRRT sessions per week (possible range: 1 to 7). As categorical variables, we created RRT dose categories based on the literature, as well as standard statistical groupings (median, tertiles). Posthoc multivariate analyses were also performed limiting the analysis to specific subgroups of CRRT patients (septic patients, by simplified acute physiology score (SAPS) scores, ≥ 25 hours of CRRT). Because of the relatively small sample size of the IRRT, subgroup analysis was not performed.

Finally, ICU survival by RRT dose categories was presented graphically using Kaplan-Meier product limit survival plot. Two-tailed p values less than 0.05 were considered significant. Statistical analyses were conducted using STATA 10 (StataCorp LP, College Station, TX, USA).

Results

Enrollment and baseline characteristics

Characteristics of the participating centres are shown in Table 1 in Additional data file 2. The median enrollment period in each study centre was 384 days. During the study period, about 15,200 patients were admitted to participating ICUs. Among them, 757 patients were treated with RRT sometime during the ICU stay (Figure 1). Of the 757 enrolled patients, we excluded patients (n = 19) who received concomitant extracorporeal treatments (e.g. endotoxin adsorption) other than those specified in the methods of this report, and those with incomplete data (n = 117). The majority of incomplete data was due to one missing datapoint needed to calculate RRT dose on a specific day, such as percentage pre-dilution or actual start or stop time. Complete data on pre-specified outcomes were not available for 11 patients (1.4%).
Table 1

Clinical characteristics of ICU patients receiving RRT

 

All

CRRT

IRRT

Mixed RRT

P CRRT vs IRRT

P (three groups)

n (%)

471

338 (72)

87 (18)

46 (10)

  

Male sex (%)

67.7

66.6

70.1

71.7

0.529

0.679

Age (years)

63.6 ± 16.2

62.1 ± 16.9

68.3 ± 13

65.8 ± 14.7

0.004

0.009

Body weight (kg)

79.3 ± 19.3

79.4 ± 19.7

77.9 ± 19.6

81.4 ± 15

0.269

0.229

ICU admission

      

   SAPS II

50 ± 18

50 ± 17

50 ± 19

51 ± 21

0.508

0.788

   SOFA

10 ± 4

10 ± 3

10 ± 3

11 ± 4

0.703

0.012

   Creatinine (μmol/L)

99(80 to 150)

100 (80 to 150)

106 (80 to 177)

97 (80 to 115)

0.277

0.278

   Chronic kidney disease (%)

56.3

55.9

55.2

60.9

0.901

0.796

Diagnosis

      

   Sepsis (%)

32.7

38.8

14.9

21.7

< 0.001

< 0.001

   Post-surgical (%)

29.7

21.9

51.7

45.7

< 0.001

< 0.001

Admission department

      

   Emergency (%)

30.4

33.4

19.5

28.3

0.012

0.040

   Medicine (%)

21.0

24.0

12.6

15.2

0.022

0.041

   Surgery (%)

48.6

42.6

67.8

56.5

< 0.001

< 0.001

   Hospital to ICU admission (days)

1 (0 to 5)

1 (0 to 4)

2 (0 to 7)

1 (0 to 5)

0.042

0.146

RRT

      

   ICU admission to start RRT (days)

3 (1 to 7)

2 (1 to 7)

3.5 (1 to 8.5)

3 (2 to 5)

0.884

0.700

   RIFLE class at RRT initiation

      

Risk (%)

11.3

12.7

5.8

10.9

0.067

0.186

Injury (%)

28.5

27.5

31.0

30.4

0.515

0.746

Failure (%)

57.3

56.8

60.9

54.3

0.489

0.759

Non-renal indication (%)

2.8

3.0

2.3

2.2

0.740

0.920

   SOFA at RRT initiation

11 ± 3

12 ± 3

10 ± 2

13 ± 3

< 0.001

< 0.001

   Creatinine at RRT initiation (μmol/L)

265 (177 to 368)

274 (177 to 380)

243 (203 to 301)

194 (141 to 309)

0.319

0.031

   Start to end RRT (days)

3 (2 to 7)

3 (2 to 6)

4 (2 to 7)

13.5 (7 to 26.5)

0.113

< 0.001

Indication for RRT initiation

      

   Azotaemia

72.1

67.9

86.2

76.1

0.001

0.003

   RIFLE class

64.4

64.9

60.9

67.4

0.495

0.715

   Fluid overload

58.6

61.6

51.7

50.0

0.096

0.116

   Oliguria

43.6

48.1

28.7

39.1

0.001

0.004

Outcome

      

   ICU mortality (%)

47.6

54.1

22.1

44.7

< 0.001

< 0.001

   Mechanical ventilation (days)

10 (3 to 19)

10 (4 to 19)

8 (1 to 17)

16 (11 to 38)

0.037

0.002

   ICU length of stay (days)

14 (7 to 27)

13 (6.5 to 26)

14 (6 to 23)

25 (15 to 42)

0.769

< 0.001

CRRT = continuous renal replacement therapy; ICU = intensive care unit; IRRT = intermittent renal replacement therapy; RIFLE = Risk-Injury-Failure-Loss-Endstage renal disease; RRT = renal replacement therapy; SAPS II = simplified acute physiology score; SOFA = sequential organ failure assessment.

Among the remaining 553 AKI patients, 419 received CRRT only, 88 received IRRT only and 46 were treated with mixed RRT schedules (IRRT, CRRT, coupled plasmafiltration adsorption). As patients in this last group crossed over from one RRT modality to another, delivered dose could not be calculated due to lack of clinically validated models, and they were excluded from the analysis. Among patients treated on only one RRT schedule (either continuous only or intermittent only), 82% received CRRT. This proportion represents current practice in Europe as previously reported. Out of 419 CRRT patients, 81 patients had at least one interruption of 18 hours or more, and then resumed CRRT [14]. The median interruption time was 49 hours (IQR = 29 to 113), predominantly due to filter clotting, disconnection for procedures and change in patient clinical status (e.g. CRRT not required in a window period). As daily CRRT dose would appear artificially low in this situation, such patients were not included in the analysis. Eighty eight patients (18%) were treated exclusively with IRRT. One patient had only three IRRT sessions over a span of 146 days, and was excluded from analysis (Figure 1).

Characteristics of the study population are described in Table 1. CRRT patients were younger, more likely to have sepsis, more likely to have been admitted directly into the ICU from the emergency room and less likely to be surgical patients. The mean serum creatinine at RRT initiation was 265 μmol/L. Nearly 60% of all patients were in RIFLE class Failure at RRT initiation. A small minority of patients did not meet criteria even for Risk, and were labelled as a non-renal indication (e.g. volume overload). Among the reasons cited to start RRT, azotaemia was significantly more common in the IRRT group, and oliguria in the CRRT group. Crude ICU mortality was 54% in the CRRT group, 22% in the IRRT group and 45% in the mixed group.

Patient characteristics by RRT dose

CRRT

In the CRRT group, the median delivered RRT dose was 27.1 ml/kg/hour (IQR = 22.1 to 33.9). Only 75 patients (22%) received more-intensive dose (≥ 35 ml/kg/hour), while 262 (78%) received less-intensive CRRT. In further detail, 202 (60%) received a dose between 21 and 34 ml/kg/hour, and 61 (18%) received a dose of 20 ml/kg/hour or less (Table 2). Patients were also divided into tertiles of RRT dose (Table 2 in Additional data file 2). Median treatment downtime, i.e. the amount of time the CRRT was not running in a 24-hour period, was one hour (IQR = 0 to 2). The most common causes for CRRT interruption were clotting of the circuit (74% of episodes), vascular access problem (11%) and clinical reasons (10%). The median prescribed CRRT dose was estimated at 34.3 ml/kg/hour (IQR = 27.3 to 42.9). Eighty seven percent of patients used replacement fluid in various proportions of pre-dilution (median 70%, IQR = 33 to 100). Patients receiving CRRT of 35 ml/kg/hour or above had lower body weight, higher admission SAPS II and SOFA scores, and a trend towards lower serum creatinine at RRT initiation (Table 2). The net fluid removal did not differ between the more- and less-intensive groups: the median was 852 ml/day (IQR = 221 to 1693) in more-intensive CRRT, and 928 ml/day (IQR = 428 to 1996) in less-intensive CRRT (P = 0.22).
Table 2

Clinical characteristics of CRRT patients by CRRT dose (≤ 20, 21 to 34, and ≥ 35 ml/kg/hour)

 

Less-intensive (< 35 ml/kg/hour)

More-intensive

 
 

≤ 20 ml/kg/hour

21 to 34 ml/kg/hour

≥ 35 ml/kg/hour

P

n (%)

61 (18)

202 (60)

75 (22)

 

Male sex (%)

73.8

67.8

58.1

0.139

Age (years)

59.05 ± 19.0

63.48 ± 15.9

61.01 ± 17.4

0.226

Body weight (kg)

91.66 ± 24.4

79.70 ± 18.0

68.81 ± 12.8

< 0.001

ICU admission

    

   SAPS II

46 ± 19

51 ± 17

52 ± 16

0.030

   SOFA

9 ± 4

10 ± 3

11 ± 4

0.030

   Creatinine (μmol/L)

106 (88 to 150)

97 (80 to 150)

106 (80 to 150)

0.597

   Chronic kidney disease (%)

47.5

58.9

55.4

0.290

Diagnosis

    

   Sepsis (%)

31.2

40.1

40.5

0.419

   Post-surgical (%)

24.6

21.3

21.6

0.859

Admission department

    

   Emergency (%)

36.1

35.2

25.7

0.292

   Medicine (%)

16.4

23.3

32.4

0.087

   Surgery (%)

47.5

41.6

41.9

0.702

   Hospital to ICU admission (days)

0.5 (0 to 4)

1 (0 to 4)

1 (0 to 3)

0.654

RRT

    

   ICU admission to RRT (days)

2.5 (2 to 8)

3 (2 to 7)

2 (1 to 3)

0.005

   RIFLE class at RRT initiation

    

Risk (%)

19.7

9.9

13.5

0.123

Injury (%)

18.0

27.7

35.1

0.086

Failure (%)

55.7

59.9

50.0

0.331

Non-renal indication (%)

6.6

2.5

1.4

0.168

   SOFA at RRT initiation

11 ± 3

12 ± 3

12 ± 3

0.068

   Creatinine at RRT initiation (μmol/L)

283 (177 to 389)

283 (194 to 415)

221 (168 to 327)

0.052

   CRRT dose (ml/kg/hour)

15.4 ± 4.2

26.9 ± 4.0

44.8 ± 9.4

< 0.001

   Start to end RRT (days)

3 (2 to 6)

4 (2 to 8)

2 (1 to 3)

< 0.001

Indication for RRT initiation

    

   Azotaemia

65.0

70.0

63.9

0.559

   RIFLE class

56.7

70.0

56.9

0.048

   Fluid overload

61.7

62.5

59.7

0.917

   Oliguria

49.5

41.7

48.6

0.562

Outcome

    

   ICU mortality (%)

50.8

53.0

60.8

0.426

   Mechanical ventilation (days)

13 (3 to 23)

12 (5 to 20)

5 (2.5 to 13)

< 0.001

   ICU length of stay (days)

17 (7.5 to 29)

15 (9 to 27)

8 (4 to 18)

< 0.001

CRRT = continuous renal replacement therapy; ICU = intensive care unit; RIFLE = Risk-Injury-Failure-Loss-Endstage renal disease; RRT = renal replacement therapy; SAPS II = simplified acute physiology score; SOFA = sequential organ failure assessment.

IRRT

In the IRRT group (Table 3), the median delivered dose was 7 sessions/week (IQR = 5 to 7). Fifty six patients (64%) received more-intensive IRRT, while 31 (36%) were treated with the less-intensive dose. In further detail, 51 patients (59%) received daily dialysis, while five (6%) had 6 sessions/week, 10 (11%) had five sessions/week and 21 (24%) received alternate day dialysis (3 to 4 sessions/week). The median dialysis duration was 5.5 (IQR = 4 to 9) hours. The median prescribed Kt/V per session was estimated at 1.2 (IQR = 0.8 to 1.9). More-intensive IRRT patients were more likely to be septic compared with the less-intensive group (Table 3). The net fluid removal was similar between the more- and less-intensive groups: the median was 780 ml/day (IQR = 410 to 1115) in more-intensive IRRT, and 829 ml/day (IQR = 485 to 1103) in less-intensive IRRT (P = 0.68).
Table 3

Clinical characteristics of IRRT patients by IRRT dose (< 6 and ≥ 6 sessions per week)

 

Frequency < 6 days/week

Frequency ≥ 6 days/week

P

n (%)

31 (36)

56 (64)

 

Male sex (%)

71.0

69.6

0.897

Age (years)

69.13 ± 11.7

67.84 ± 13.7

0.873

Body weight (kg)

79.52 ± 15.7

76.99 ± 21.6

0.246

ICU admission

   

   SAPS II

49 ± 15

50 ± 20

0.958

   SOFA

10 ± 3

9 ± 4

0.689

   Creatinine (μmol/L)

106 (80 to 186)

106 (80 to 177)

0.822

   Chronic kidney disease (%)

54.8

55.4

0.963

Diagnosis

   

   Sepsis (%)

3.2

21.4

0.023

   Post-surgical (%)

64.5

44.6

0.076

Admission department

   

   Emergency (%)

12.9

23.2

0.245

   Medicine (%)

12.9

12.5

0.957

   Surgery (%)

74.2

64.3

0.343

   Hospital to ICU admission (days)

3 (0 to 8)

1 (0 to 6)

0.322

RRT

   

   ICU admission to RRT (days)

5 (1 to 11)

3 (1 to 7)

0.351

   RIFLE class at RRT initiation

   

Risk (%)

6.5

5.4

0.834

Injury (%)

41.9

25.0

0.102

Failure (%)

51.6

66.1

0.186

Non renal indication (%)

0.0

3.6

0.287

   SOFA at RRT initiation

10 ± 2

10 ± 2

0.941

   Creatinine at RRT initiation (μmol/L)

247 (199 to 296)

234 (212 to 301)

0.880

   Number of sessions per week

4.5 ± 0.8

6.9 ± 0.2

< 0.001

   Start to end RRT (days)

6 (5 to 12)

3 (1 to 5)

< 0.001

Indication for RRT initiation

   

   Azotaemia

96.8

80.4

0.033

   RIFLE class

58.1

62.5

0.685

   Fluid overload

41.9

57.1

0.174

   Oliguria

22.6

32.1

0.345

Outcome

   

   ICU mortality (%)

19.4

23.6

0.646

   Mechanical ventilation (days)

14 (5 to 21)

6 (0 to 14)

0.030

   ICU length of stay (days)

18 (13 to 31)

9.5 (6 to 18)

0.023

ICU = intensive care unit; IRRT = intermittent renal replacement therapy; RIFLE = Risk-Injury-Failure-Loss-Endstage renal disease; RRT = renal replacement therapy; SAPS II = simplified acute physiology score; SOFA = sequential organ failure assessment.

Outcomes

CRRT

On univariate analysis, age, SAPS II, SOFA score and serum creatinine on admission, SOFA score and serum creatinine on RRT initiation, and RRT duration were significantly associated with ICU mortality. On multivariate analysis, CRRT dose was not associated with ICU mortality (Table 4). Further adjustment for the propensity score did not significantly alter this result (adjusted odds ratio (OR) = 1.40, 95% confidence interval (CI) = 0.74 to 2.65). Kaplan Meier curves are shown in Figures 2 and 3 in Additional data file 2. Results were similar whether CRRT dose was expressed as a continuous or categorical variable (Table 5). Additional post-hoc sensitivity analyses were performed (Table 6). Results were similar in patients with and without sepsis. We also performed subgroup analysis on the following patient subgroups: those with intermediate severity of illness (SAPS II scores from 45 to 60), and those who had a minimum exposure of 25 hours for CRRT therapy.
Table 4

Unadjusted and covariate adjusted analysis for ICU mortality in CRRT patients

CRRT

Unadjusted analysis

Covariate adjusted analysis

 

OR

95% CI

P

OR

95% CI

P

Male sex

1.47

0.91 to 2.37

0.097

1.86

1.11 to 3.12

0.019

Age (10-year increments)

1.34

1.17 to 1.52

< 0.001

1.42

1.22 to 1.64

< 0.001

SOFA at RRT initiation

1.18

1.09 to 1.28

< 0.001

1.20

1.10 to 1.30

< 0.001

Creatinine at RRT initiation (μmol/L)

0.85

0.76 to 0.95

0.005

0.79

0.69 to 0.90

0.001

Downtime

0.90

0.80 to 1.01

0.081

0.95

0.83 to 1.07

0.386

More-intensive (≥ 35 ml/kg/hour)

1.41

0.83 to 2.38

0.204

1.21

0.66 to 2.21

0.537

CI = confidence interval; CRRT = continuous renal replacement therapy; ICU = intensive care unit; OR = odds ratio; RRT = renal replacement therapy; SOFA = sequential organ failure assessment.

Table 5

Sensitivity analysis for ICU mortality in CRRT patients

CRRT dose expressed as

Unadjusted OR with 95% CI

Pvalue

Adjusted OR with 95% CI

Pvalue

Raw value (ml/kg/hour)

1.00 (0.98 to 1.02)

0.827

0.99 (0.97 to 1.02)

0.583

Increment of 10 ml/kg/hour

1.05 (0.87 to 1.26)

0.638

0.98 (0.79 to 1.23)

0.879

Literature cut-offs

    

   ≤ 20 ml/kg/hour (ref.)

1.00

 

1.00

 

   21 to 34 ml/kg/hour

1.09 (0.61 to 1.93)

0.768

0.79 (0.40 to 1.55)

0.492

   ≥ 35 ml/kg/hour

1.50 (0.76 to 2.98)

0.245

1.00 (0.45 to 2.24)

0.995

Less-intensive (< 35 ml/kg/hour) (ref.)

1.00

 

1.00

 

More-intensive (≥ 35 ml/kg/hour)

1.41 (0.83 to 2.38)

0.204

1.21 (0.66 to 2.21)

0.537

≤ 20 ml/kg/hour (ref.)

    

> 20 ml/kg/hour

1.19 (0.68 to 2.07)

0.546

0.84 (0.43 to 1.61)

0.595

Tertiles

    

   1st tertile (≤ 23.5 ml/kg/hour) (ref.)

1.00

 

1.00

 

   2nd tertile (23.6 to 30.9 ml/kg/hour)

0.71 (0.42 to 1.20)

0.206

0.67 (0.37 to 1.23)

0.196

   3rd tertile (≥ 31 ml/kg/hour)

1.32 (0.78 to 2.24)

0.306

1.11 (0.60 to 2.06)

0.734

   1st+2nd tertiles (ref.)

    

   3rd tertile

1.56 (0.98 to 2.48)

0.058

1.36 (0.79 to 2.32)

0.268

Median

    

   < Median (ref.)

1.00

 

1.00

 

   ≥ Median (≥ 27.1 ml/kg/hour)

0.99 (0.64 to 1.51)

0.945

0.82 (0.49 to 1.35)

0.433

CRRT dose in first 24 hours

    

   Less-intensive (< 35 ml/kg/hour) (ref.)

1.00

 

1.00

 

   More-intensive (≥ 35 ml/kg/hour)

1.02 (0.65 to 1.62)

0.918

0.96 (0.57 to 1.60)

0.866

CRRT dose in first 48 hours

    

   Less-intensive (< 35 ml/kg/hour) (ref.)

1.00

 

1.00

 

   More-intensive (≥ 35 ml/kg/hour)

1.08 (0.68 to 1.74)

0.737

1.03 (0.60 to 1.76)

0.915

CI = confidence interval; CRRT = continuous renal replacement therapy; ICU = intensive care unit; OR = odds ratio.

Table 6

Subgroup analysis for ICU mortality in CRRT patients

More-intensive vs less-intensive CRRT dose*

Unadjusted OR* with 95% CI

Pvalue

Adjusted OR* with 95% CI

Pvalue

Patient subgroups

    

Sepsis

1.64 (0.70 to 3.85)

0.259

1.91 (0.71 to 5.13)

0.198

Non sepsis

1.27 (0.65 to 2.48)

0.488

0.95 (0.43 to 2.10)

0.896

SAPS II 45 to 60

1.03 (0.44 to 2.40)

0.945

0.67 (0.24 to 1.81)

0.428

SAPS II < 45 or > 60

1.69 (0.85 to 3.31)

0.129

1.76 (0.80 to 3.86)

0.159

≥ 25 hours of CRRT

1.06 (0.55 to 2.01)

0.870

1.07 (0.51 to 2.28)

0.855

< 25 hours of CRRT

1.72 (0.61 to 4.86)

0.303

1.12 (0.34 to 3.73)

0.854

*OR refers to more-intensive CRRT with respect to the reference group less-intensive CRRT.

CI = confidence interval; CRRT = continuous renal replacement therapy; ICU = intensive care unit; OR = odds ratio; SAPS II = simplified acute physiology score.

Similarly, there was no relation between CRRT dose and ICU mortality in these two subgroups. Patients who received more-intensive CRRT overall had shorter duration of mechanical ventilation and ICU stay (Table 7). Among survivors, there was a trend towards shorter ICU stay (P = 0.063), while duration of mechanical ventilation was significantly less (P = 0.031). Similar to the overall group, survivors in the more-intensive CRRT group had significantly lower body weight and shorter ICU stay prior to CRRT initiation (2 days, IQR = 1 to 3; vs. less-intensive 3 days, IQR = 2 to 7.5; P = 0.002), compared with the less-intensive CRRT group. Otherwise, the survivors in the two groups had similar baseline characteristics.
Table 7

ICU length of stay and ventilation days by RRT dose

 

Total

CRRT

  

< 35 ml/kg/hour

≥ 35 ml/kg/hour

P

Length of ICU stay (days)

13 (6.5 to 26)

15 (9 to 28)

8 (4 to 18)

< 0.001

   Patients who survived

19 (11 to 32)

19.5 (12 to 33.5)

15 (8 to 26)

0.063

   Patients who died

10 (4 to 19)

12 (6 to 20)

4.5 (3 to 9.5)

< 0.001

Duration of MV (days)

10 (4 to 19)

12 (5 to 21)

5 (2.5 to 13)

< 0.001

   Patients who survived

14 (4.5 to 22)

14 (5 to 24)

7 (4 to 17)

0.031

   Patients who died

8.5 (3 to 17)

10 (5 to 18)

4 (2 to 9.5)

< 0.001

  

IRRT

 

Total

Frequency < 6 sessions/week

Frequency ≥ 6 sessions/week

P

Length of ICU stay (days)

14 (6.5 to 23)

18 (15 to 31)

9.5 (6 to 18)

0.023

   Patients who survived

11 (6 to 20)

18 (13 to 35)

8 (5.5 to 14)

0.008

   Patients who died

17 (12 to 23)

18 (17 to 23)

15 (12 to 22)

0.597

Duration of MV (days)

8 (1 to 17)

14 (5 to 21)

6 (0 to 14)

0.030

   Patients who survived

5 (0 to 13)

12 (3 to 24)

2.5 (0 to 10)

0.026

   Patients who died

17 (11 to 21)

18 (17 to 21)

14 (8 to 18)

0.252

Data shown as median (interquartile range).

CRRT = continuous renal replacement therapy; ICU = intensive care unit; IRRT = intermittent renal replacement therapy; MV = mechanical ventilation.

IRRT

None of the variables examined, including IRRT dose, were significantly associated with ICU mortality on univariate and multivariate analysis (Table 8). This was seen whether IRRT dose was expressed as a dichotomous variable (more- vs. less-intensive) or as a continuous variable, i.e. number of sessions per week (unadjusted OR = 1.11, 95% CI = 0.74 to 1.69). Because of the relatively small sample size, no further sensitivity analysis was attempted. Patients who received more-intensive IRRT had shorter duration of mechanical ventilation and ICU stay, particularly among survivors (Table 7). Survivors in the more-intensive IRRT group were more likely to have sepsis (23% vs. less-intensive 0%, P = 0.008), compared with the less-intensive IRRT group. Otherwise, the survivors in the two groups had similar baseline characteristics.
Table 8

Unadjusted and covariate adjusted analysis for ICU mortality in IRRT patients

IRRT

Unadjusted analysis

Covariate adjusted analysis

 

OR

95% CI

P

OR

95% CI

P

Male sex

1.28

0.37 to 5.12

0.674

1.38

0.42 to 4.58

0.598

Age (10-year increments)

1.31

0.85 to 2.01

0.216

1.29

0.83 to 2.02

0.260

RIFLE class

      

   Risk (%)

2.51

0.19 to 23.49

0.320

1.00

  

   Injury (%)

2.45

0.74 to 7.92

0.089

1.29

0.2 to 8.33

0.790

   Failure (%)

0.38

0.12 to 1.22

0.064

0.46

0.07 to 2.88

0.408

   More-intensive (≥ 6 sessions/week)

1.29

0.43 to 3.82

0.646

1.50

0.48 to 4.67

0.482

CI = confidence interval; ICU = intensive care unit; IRRT = intermittent renal replacement therapy; OR = odds ratio; RIFLE = Risk-Injury-Failure-Loss-Endstage renal disease.

Discussion

We conducted a European multicentre observational study to describe clinical outcomes associated with RRT dose in critically ill patients with AKI. The key findings of this study are the following. First, despite a prescribed CRRT dose approximating 35 ml/kg/hour, the recommended 'minimum' for critically ill AKI patients according to expert opinion [10, 24], the delivered CRRT dose was markedly lower than this value. Second, it appears that alternate day IRRT for critically ill patients is uncommon in the participating centres. Third, after adjustment for multiple variables, we did not observe a beneficial effect of more-intensive RRT dose on ICU survival. Fourth, ICU stay and ventilation days were shorter in the more-intensive RRT groups.

Our findings on mortality are congruent with an international observational study [25] and two recent randomised clinical trials on standard versus higher-dose CVVHDF including the large multicentre Veterans Affairs/National Institute of Health (VA/NIH) trial in the US [8, 9]. There are conflicting results on the effect of RRT dose on patient outcome. Two earlier single-centre randomised clinical trials showed a beneficial effect of an intensive CRRT dose when compared with a less-intensive dose in both CVVH (≥ 35 ml/kg/hour versus ≤ 20 ml/kg/hour) [4] and CVVHDF (≥ 42 ml/kg/hour versus ≤ 25 ml/kg/hour) [7]. In contrast, Bouman and colleagues did not detect any difference in outcome between ultrafiltration rates of 3 to 4 l/hour and 1 to 1.5 l/hour; however, this study suffered from lack of power and an unexpectedly high ICU survival rate among enrolled subjects [5]. Interestingly, in contrast to other studies [5, 79], we observed a positive effect of more-intensive RRT dose on ICU stay and duration of mechanical ventilation.

Our study has several notable features. It is the first large observational study specifically oriented towards RRT dose involving multiple ICUs which are a mix of academic and non-academic centres. As such, it is likely to be more reflective of actual clinical practice and a broad patient population. Indeed, in the CRRT group, the prevalence of sepsis was 39% and the overall mortality was 54%. This is similar to that described in the literature [3, 6, 7, 9, 22].

Second, it focused on delivered, rather than prescribed, RRT dose. This is not a minor point, as many factors contribute to delivering a RRT dose lower than prescribed, and it is the delivered dose which the patient 'sees' and which is likely to affect the clinical outcome. A prior observational study reported only on prescribed, but not the delivered, CRRT dose [25]. Furthermore, ours is the first dose study in which correction for percentage predilution was performed in the calculation of CRRT dose, resulting in a more accurate estimate. It has been shown that delivered dialysis dose is generally lower than prescribed, ranging from 68 to 89% of prescribed [7, 8, 26, 27].

Third, we specifically collected information on treatment 'downtime', which is considered an important factor affecting delivered RRT dose.

Fourth, it is also one of only two studies to look at a continuum of RRT dose so far [25]. Of note, the majority of patients received a CRRT dose which was in between the 'standard/low dose' and the 'high dose' arms evaluated in randomised clinical trials [4, 79]. Whether having several patients in this 'intermediate' zone served to dilute the true clinical effect of RRT dose remains unclear. It has been suggested that only major changes in the application of dose can be reasonably expected to have a discernible clinical effect [28]. For example, the difference between a delivered CRRT dose of 30 and 35 ml/kg/hour may be too subtle, or could be criticised for being within a calculation error. However, we performed a variety of analyses which included expressing dose in increments of 10 ml/kg/hour (arbitrarily considered a 'significant' increment), or as categories based on cut-offs from the literature or on statistical spread (e.g. tertiles, median), and failed to find a significant effect on ICU mortality (Table 5). It is also possible that therapy in the first 24 to 48 hours is more crucial with respect to patient outcome. We therefore performed a post-hoc sensitivity analysis looking at CRRT dose during these periods (Table 5), and this did not significantly alter the results.

It has been suggested that septic patients may be a specific population which could benefit from higher RRT dose [4, 11]. In our post-hoc analysis, the effect of RRT dose on mortality was similar in both septic and non-septic patients (Table 6). It is also possible that more-intensive RRT only benefits patients with an intermediate severity of illness, as suggested by Paganini and colleagues [29]. We performed two sensitivity analyses to address this. First, we limited the analysis only to patients with SAPS scores between 45 and 60, in whom the predicted mortality ranges from 35 to 60%. In five studies evaluating the effects of CRRT dose, mean acute physiology and chronic health evaluation (APACHE) II scores ranged from 22 to 26, giving predicted mortality rates of 42 to 57% in this group [49]. Our results were similar within this subgroup. Second, patients may have a very short duration of RRT for various reasons. For example, they may be gravely ill and die shortly after RRT initiation. Alternatively, they may be less ill and have rapid recovery of renal function allowing early withdrawal of RRT. Therefore, we performed a secondary analysis looking only at patients who had at least 25 hours of RRT. This was adapted from the definition of an 'adequate trial of therapy' in a randomised trial comparing CRRT and IRRT [30]. The results remained qualitatively unchanged.

This study provides further insight into the prescription and delivery of RRT dose in current clinical practice. There is a gap between prescribed and delivered CRRT dose, as has been shown by others [7, 8, 26, 27]. Treatment downtime is a known contributing factor. In contrast to earlier studies, however, we also considered the effect of percentage pre-dilution in calculating the delivered dose. We hypothesise that lack of attention to this when prescribing CRRT may play a heretofore unrecognised role in under-delivery of dose. As modern machines are able to provide replacement fluid in variable proportions of pre/post-dilution, it is important to keep this in mind. We also observed that CRRT patients receiving more-intensive dose had significantly lower body weights. This may represent indiscriminate 'by the litre' prescription, rather than 'individualised' prescription based on body weight [13]. It is also possible that it is simply more difficult to provide higher doses in larger patients with currently available technology. Perhaps the greatest concern arising from the observed gap between prescription and delivery is the potential downstream effect of prescribing 20 ml/kg/hour to patients. There would be a real risk of effectively underdialysing patients [31].

We acknowledge certain limitations in this study. As with all observational studies, ours may have suffered from 'selection by prognosis' [32]. Indeed, it is quite plausible that, based on existing literature, the treating intensivist or nephrologist would prescribe a higher RRT dose to a sicker patient, who a priori has a higher predicted mortality. Although we adjusted for potential confounders, including propensity score analysis (Table 3 in Additional data file 2), this may still be insufficient because it is not possible to adjust for confounders that are neither measured nor known. We also chose to exclude a number of patients from the analysis, which may have resulted in some selection bias. It was not possible to analyse patients who crossed over between modalities because there is no single equivalent expression of dose clinically validated for both CRRT and IRRT. However, when we compared the analysed group to the overall population, they were similar in terms of demographics, general severity of illness and co-morbidities. Therefore, if selection bias was present, its effect is likely to be minimal. For IRRT patients, we were unable to correlate outcome with the measured Kt/V, as the necessary laboratory parameters for the calculation were not collected as part of routine practice. This is consistent with the findings of the VA/NIH group in their pre-trial survey that assessment of the delivered dose of IRRT was performed infrequently in clinical practice [13]. Nevertheless, we believe we have a reasonable estimate of prescribed IRRT dose based on the operational parameters collected, with a median prescribed Kt/V of 1.2. Although we found an inverse relationship between RRT dose and duration of mechanical ventilation, as well as with ICU stay, we acknowledge that there were no standard criteria for extubation or ICU discharge in this observational study. Furthermore, we only looked at short-term outcomes. Future studies should attempt to better understand the long-term effects of RRT dose. Lastly, this was a voluntary survey conducted in predominantly CRRT-oriented centres. As such, it may not be possible to generalise the results to other medical centres. It is noteworthy, however, that despite being CRRT-oriented centres, the delivered CRRT dose, although higher than reported in prior studies [26, 28], still fell short of the mark. This begs the question as to whether a dose of 35 ml/kg/hour or 45 ml/kg/hour [4, 11], as suggested for septic patients, is routinely achievable in the real world.

Nevertheless, our findings of reduced ICU stay and mechanical ventilation days with more-intensive RRT may potentially have a large impact on health resource utilisation, if confirmed by future studies. For example, the average total cost per ICU day has been estimated at €1200 in a sample of European countries [33]. A possible implication would be potential savings of €8000 to 10,200 per ICU admission with more-intensive RRT. In contrast to our results, two other studies showed no significant difference in duration of mechanical ventilation between lower and higher CRRT dose groups [5, 7]; however, this issue was not specifically addressed by others [4, 6, 8, 9].

This study highlights that the concept of RRT dose or adequacy is more complex than previously thought. This adds fuel to the debate on the optimal RRT dose for critically ill patients with AKI. Clearly there are other dimensions to RRT adequacy other than removal of various solutes, whether expressed as Kt/V, ml/kg/hour or number of RRT sessions per week. These include prophylactic volume control, as well as acid-base and tonicity control, among others. Furthermore, recognising that critical illness is not a static condition, a 'dynamic approach' to RRT dose, rather than fixed dose, may be more appropriate in this setting [34]. This hypothesis is worthy of exploration in future studies. In addition, it is likely that there are multifaceted interactions between RRT dose and other factors (timing of RRT, modality, patient characteristics, etc.) which influence outcome.

Conclusions

We conducted a prospective European multicentre cohort study of AKI patients treated with RRT. This study provides insight in to how RRT is currently practiced in the ICU. We observed that the median CRRT dose is lower than 35 ml/kg/hour and only 22% of patients received this or a higher dose. In contrast, 60% of IRRT patients were treated daily. We evaluated the association between actual delivered RRT dose and clinical outcomes. The data provide no evidence for a survival benefit afforded by more-intensive RRT. However, higher RRT dose appeared to be associated with shorter ICU stay and duration of mechanical ventilation. In conclusion, within the confines of the dose range examined, there was no effect on survival while effects on non-mortality endpoints should be examined by further study.

Key messages

  • In this observational study, the delivered CRRT dose was markedly lower than 35 ml/kg/hour (median = 27).

  • Alternate day IRRT for critically ill patients was uncommon in the participating centres.

  • After adjustment for multiple variables, there was no beneficial effect of more-intensive RRT dose on ICU survival.

  • Shorter ICU stay and duration of mechanical ventilation were observed in the more-intensive RRT groups.

Notes

Abbreviations

AKI: 

acute kidney injury

APACHE: 

acute physiology and chronic health evaluation

CI: 

confidence interval

CRRT: 

continuous renal replacement therapy

CVVH: 

continuous veno-venous haemofiltration

CVVHD: 

continuous veno-venous haemodialysis

CVVHDF: 

continuous veno-venous haemodiafiltration

ICU: 

intensive care unit

IRRT: 

intermittent renal replacement therapy

IQR: 

interquartile range

RIFLE: 

Risk-Injury-Failure-Loss-Endstage renal disease

RRT: 

renal replacement therapy

SAPS II: 

simplified acute physiology score

SOFA: 

sequential organ failure assessment.

Declarations

Acknowledgements

Fresenius Medical Care (Western European Medical and Scientific Coordination) provided technical support and internet services for web-based data collection and supported the organisation of the Steering and Scientific Committees. It did not influence the study design, data interpretation or writing of the report. The authors would like to thank Irene Bolgan for her invaluable assistance with the statistical analysis. The corresponding author had full access to all data in the study and had final responsibility for the decision to submit for publication. Agreement to submit for publication was obtained from all authors.

Participating centres and physicians

Austria: Innsbruck (M. Ioannidis); Belgium: Saint-Pierre Para-Universitary Hospital, Ottignies-Louvain-La-Neuve (P. Honoré); France: Medical ICU, University of Poitiers, CHU Poitiers, Poitiers (R. Robert, J. Voultoury), CH Lens (PP Thevenin), Hopital de Maubeuge (V. Labiotte), University Hospital of Bordeaux (O. Joannes-Boyau); Germany: University of Düsseldorf, Düsseldorf (D. Kindgen-Milles); Italy: Riuniti di Bergamo Hospital Bergamo (E. Moretti), Maggiore Hospital, Crema (M. Cerisara), Santa Croce e Carle Hospital, Cuneo (P. Inguaggiato), Valle Camonica Hospital, Esine (W. Morandini), Department of Anaesthesiology and Intensive Care I, San Gerardo dei Tintori Hospital, Monza (R. Fumagalli, R. Rona), Niguarda Hospital, Milan, (S. Vesconi, GP Monti), IRCCS San Raffaele, Milan (S. Slaviero), CTO Hospital, Torino (F. Mariano, L. Tedeschi), Ospedale G Bosco, Torino (S. Livigni, M. Maio), Policlinico Umberto 1, Rome (Pietropaoli P., E. Alessandri); St Bortolo Hospital, Vicenza (A. Brendolan, D. Cruz); Bolognini Hospital of Seriate, Seriate (M. Marchesi); Portugal: Hospital Center of Porto, Porto (A. Marinho), Hospital Center of Tamega and Sousa – Penafiel (E. Lafuente), Hospital Center of Porto, Porto (A. Santos); Spain: Hospital de Vitoria (J. Maynar), Hospital Gral. De Catalunya, Sant Cugat del Vallés (T. Doñate, A. Leon), Hospital Carlos Haya, Malaga (M. Herrera, G. Seller-Perez), Hospital. 12 De Octubre, Madrid (Á. Montero, J. Sánchez- Izquierdo), Hospital Gregorio Marañon, Madrid (J. Luño, E Junco), Hospital De La Princesa (P. Alonso), Hospital La Fe, Valencia, (J. Cruz, J. Mol), Policlinico De Vigo, Vigo (R. Cabadas); The Netherlands: Doetimchen Hospital (J. Amman).

Authors’ Affiliations

(1)
Department of Anesthesiology and Intensive Care, Hospital Niguarda
(2)
Department of Nephrology, Dialysis and Transplantation, St Bortolo Hospital
(3)
Department of Anaesthesiology and Intensive Care I, St Gerardo dei Tintori Hospital
(4)
Anesthesiology Clinic, University of Düsseldorf
(5)
Hospital Center of Porto, Alameda do Prof. Hernâni Monteiro
(6)
Nephrology and Dialysis Unit, CTO Hospital
(7)
Department of Nephrology, Hospital Santa Croce e Carle
(8)
Department of Anaesthesiology and Intensive Care, Riuniti di Bergamo Hospital
(9)
Intensive Care Unit, University of Poitiers
(10)
Department of Intensive Care, Giovanni Bosco Hospital

References

  1. Lameire N, Van Biesen W, Vanholder R: Acute renal failure. Lancet. 2005, 365: 417-430.View ArticlePubMedGoogle Scholar
  2. Cruz DN, Bolgan I, Perazella MA, Bonello M, de Cal M, Corradi V, Polanco N, Ocampo C, Nalesso F, Piccinni P, Ronco C: North East Italian Prospective Hospital Renal Outcome Survey on Acute Kidney Injury (NEiPHROS-AKI) Investigators. North East Italian Prospective Hospital Renal Outcome Survey on Acute Kidney Injury (NEiPHROS-AKI): targeting the problem with the RIFLE Criteria. Clin J Am Soc Nephrol. 2007, 2: 418-425. 10.2215/CJN.03361006.View ArticlePubMedGoogle Scholar
  3. Uchino S, Kellum JA, Bellomo R, Doig GS, Morimatsu H, Morgera S, Schetz M, Tan I, Bouman C, Macedo E, Gibney N, Tolwani A, Ronco C: Beginning and Ending Supportive Therapy for the Kidney (BEST Kidney) Investigators. Acute renal failure in critically ill patients: a multinational, multicenter study. JAMA. 2005, 294: 813-818. 10.1001/jama.294.7.813.View ArticlePubMedGoogle Scholar
  4. Ronco C, Bellomo R, Homel P, Brendolan A, Dan M, Piccinni P, La Greca G: Effects of different doses in continuous veno-venous haemofiltration on outcomes of acute renal failure: a prospective randomized trial. Lancet. 2000, 356: 26-30. 10.1016/S0140-6736(00)02430-2.View ArticlePubMedGoogle Scholar
  5. Bouman CS, Oudemans-Van Straaten HM, Tijssen JG, Zandstra DF, Kesecioglu J: Effects of early high-volume continuous venovenous hemofiltration on survival and recovery of renal function in intensive care patients with acute renal failure: a prospective, randomized trial. Crit Care Med. 2002, 30: 2205-2211. 10.1097/00003246-200210000-00005.View ArticlePubMedGoogle Scholar
  6. Schiffl H, Lang SM, Fischer R: Daily hemodialysis and the outcome of acute renal failure. N Engl J Med. 2002, 346: 305-310. 10.1056/NEJMoa010877.View ArticlePubMedGoogle Scholar
  7. Saudan P, Niederberger M, De Seigneux S, Romand J, Pugin J, Perneger T, Martin PY: Adding a dialysis dose to continuous hemofiltration increases survival in patients with acute renal failure. Kidney Int. 2006, 70: 1312-1317. 10.1038/sj.ki.5001705.View ArticlePubMedGoogle Scholar
  8. Tolwani AJ, Campbell RC, Stofan BS, Lai KR, Oster RA, Wille KM: Standard versus high-dose CVVHDF for ICU-related acute renal failure. J Am Soc Nephrol. 2008, 19: 1233-1238. 10.1681/ASN.2007111173.PubMed CentralView ArticlePubMedGoogle Scholar
  9. VA/NIH Acute Renal Failure Trial Network, Palevsky PM, Zhang JH, O'Connor TZ, Chertow GM, Crowley ST, Choudhury D, Finkel K, Kellum JA, Paganini E, Schein RM, Smith MW, Swanson KM, Thompson BT, Vijayan A, Watnick S, Star RA, Peduzzi P: Intensity of renal support in critically ill patients with acute kidney injury. N Engl J Med. 2008, 359: 7-20. 10.1056/NEJMoa0802639.View ArticleGoogle Scholar
  10. Kellum JA, Bellomo R, Ronco C, Mehta R, Clark W, Levin NW: The 3rd International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI). Int J Artif Organs. 2005, 28: 441-444.PubMedGoogle Scholar
  11. Kellum JA, Venkataraman R: Application of blood purification to non-renal organ failure. Int J Artif Organs. 2005, 28: 445-449.PubMedGoogle Scholar
  12. Ricci Z, Ronco C, D'Amico G, De Felice R, Rossi S, Bolgan I, Bonello M, Zamperetti N, Petras D, Salvatori G, Dan M, Piccinni P: Practice patterns in the management of acute renal failure in the critically ill patient: an international survey. Nephrol Dial Transplant. 2006, 21: 690-696. 10.1093/ndt/gfi296.View ArticlePubMedGoogle Scholar
  13. Overberger P, Pesacreta M, Palevsky PM: VA/NIH Acute Renal Failure Trial Network. Management of renal replacement therapy in acute kidney injury: a survey of practitioner prescribing practices. Clin J Am Soc Nephrol. 2007, 2: 623-630. 10.2215/CJN.00780207.PubMed CentralView ArticlePubMedGoogle Scholar
  14. Kindgen-Milles D, Journois D, Fumagalli R, Vesconi S, Maynar J, Marinho A, Bolgan I, Brendolan A, Formica M, Livigni S, Maio M, Marchesi M, Mariano F, Monti G, Moretti E, Silengo D, Ronco C: Study protocol: the dose response Multicentre International Collaborative Initiative (DO-RE-MI). Crit Care. 2005, 9: R396-R406. 10.1186/cc3718.PubMed CentralView ArticlePubMedGoogle Scholar
  15. Bellomo R, Ronco C, Kellum JA, Mehta RL, Palevsky P: Acute Dialysis Quality Initiative workgroup. Acute renal failure – definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care. 2004, 8: R204-212. 10.1186/cc2872.PubMed CentralView ArticlePubMedGoogle Scholar
  16. Dose response Multicentre International Collaborative Initiative (DO-RE-MI) website. [http://www.acutevision.net]
  17. Keshaviah P, Nolph K, Van Stone J: The peak concentration hypothesis: a urea kinetic approach to comparing the adequacy of continuous ambulatory peritoneal dialysis and hemodialysis. Perit Dial Int. 1989, 9: 257-260.PubMedGoogle Scholar
  18. Gotch F: The current place of urea kinetic modelling with respect to different dialysis schedule. Nephrol Dial Transplant. 1998, 13 (Suppl 6): 10-14. 10.1093/ndt/13.suppl_6.10.View ArticlePubMedGoogle Scholar
  19. Casino F, Lopez F: The equivalent renal urea clearance: a new parameter to asses dialysis dose. Nephrol Dial Transplant. 1996, 11: 1574-1581.View ArticlePubMedGoogle Scholar
  20. Ricci Z, Salvatori G, Bonello M, Pisitkun T, Bolgan I, D'Amico G, Dan M, Piccinni P, Ronco C: In vivo validation of the adequacy calculator for continuous renal replacement therapies. Crit Care. 2005, 9: R266-273. 10.1186/cc3517.PubMed CentralView ArticlePubMedGoogle Scholar
  21. Uchino S, Bellomo R, Kellum JA, Morimatsu H, Morgera S, Schetz MR, Tan I, Bouman C, Macedo E, Gibney N, Tolwani A, Oudemans-Van Straaten HM, Ronco C: Beginning and Ending Supportive Therapy for the Kidney (B.E.S.T. Kidney) Investigators Writing Committee. Patient and kidney survival by dialysis modality in critically ill patients with acute kidney injury. Int J Artif Organs. 2007, 30: 281-292.PubMedGoogle Scholar
  22. Cho KC, Himmelfarb J, Paganini E, Ikizler TA, Soroko SH, Mehta RL, Chertow GM: Survival by dialysis modality in critically ill patients with acute kidney injury. J Am Soc Nephrol. 2006, 17: 3132-3138. 10.1681/ASN.2006030268.View ArticlePubMedGoogle Scholar
  23. Braitman LE, Rosenbaum PR: Rare outcomes, common treatments: analytic strategies using propensity scores. Ann Intern Med. 2002, 137: 693-695.View ArticlePubMedGoogle Scholar
  24. Kellum JA: Renal replacement therapy in critically ill patients with acute renal failure: does a greater dose improve survival?. Nat Clin Pract Nephrol. 2007, 3 (3): 128-139. 10.1038/ncpneph0398.View ArticlePubMedGoogle Scholar
  25. Uchino S, Bellomo R, Morimatsu H, Morgera S, Schetz M, Tan I, Bouman C, Macedo E, Gibney N, Tolwani A, Oudemans-van Straaten H, Ronco C, Kellum JA: Continuous renal replacement therapy: a worldwide practice survey. The beginning and ending supportive therapy for the kidney (B.E.S.T. kidney) investigators. Intensive Care Med. 2007, 33: 1563-1570. 10.1007/s00134-007-0754-4.View ArticlePubMedGoogle Scholar
  26. Evanson JA, Himmelfarb J, Wingard R, Knights S, Shyr Y, Schulman G, Ikizler TA, Hakim RM: Prescribed versus delivered dialysis in acute renal failure patients. Am J Kidney Dis. 1998, 32: 731-738. 10.1016/S0272-6386(98)70127-1.View ArticlePubMedGoogle Scholar
  27. Venkataraman R, Kellum JA, Palevsky P: Dosing patterns for continuous renal replacement therapy at a large academic medical center in the United States. J Crit Care. 2002, 17: 246-250. 10.1053/jcrc.2002.36757.View ArticlePubMedGoogle Scholar
  28. Ricci Z, Bellomo R, Ronco C: Dose of dialysis in acute renal failure. Clin J Am Soc Nephrol. 2006, 1: 380-388. 10.2215/CJN.00520705.View ArticlePubMedGoogle Scholar
  29. Paganini EP, Tapolyai M, Goormastic M, Halstenberg W, Kozlowski L, Leblanc M, Lee JC, Moreno L, Sakai K: Establishing a dialysis therapy/patient outcome link in intensive care unit acute dialysis for patients with acute renal failure. Am J Kidney Dis. 1996, 28: S81-S89. 10.1016/S0272-6386(96)90084-0.View ArticleGoogle Scholar
  30. Mehta RL, McDonald B, Gabbai FB, Pahl M, Pascual MT, Farkas A, Kaplan RM: Collaborative Group for Treatment of ARF in the ICU. A randomized clinical trial of continuous versus intermittent dialysis for acute renal failure. Kidney Int. 2001, 60: 1154-1163. 10.1046/j.1523-1755.2001.0600031154.x.View ArticlePubMedGoogle Scholar
  31. Ronco C, Cruz D, van Straaten HO, Honore P, House A, Bin D, Gibney N: Dialysis dose in acute kidney injury: no time for therapeutic nihilism – a critical appraisal of the Acute Renal Failure Trial Network study. Crit Care. 2008, 12: 308-315. 10.1186/cc7016.PubMed CentralView ArticlePubMedGoogle Scholar
  32. Jager KJ, Stel VS, Wanner C, Zoccali C, Dekker FW: The valuable contribution of observational studies to nephrology. Kidney Int. 2007, 72: 671-675. 10.1038/sj.ki.5002397.View ArticlePubMedGoogle Scholar
  33. Burchardi H, Schneider H: Economic aspects of severe sepsis: a review of intensive care unit costs, cost of illness and cost effectiveness of therapy. Pharmacoeconomics. 2004, 22: 793-813. 10.2165/00019053-200422120-00003.View ArticlePubMedGoogle Scholar
  34. Mayner-Moliner J, Sanchez-Izqierdo-Riera J, Herrera-Guitierrez M: Renal support in critically ill patients with acute kidney injury. N Engl J Med. 2008, 359: 1960-1960.Google Scholar
  35. Suri R, Blake PG: "Adequacy of hemodialysis" in Replacement of Renal Function by Dialysis. Edited by: Hörl WH, Koch KM, Lindsay RM, Ronco C, Winchester JF. 2004, Kluwer Academic Publishers, Dordrecht, The Netherlands, 597-638.View ArticleGoogle Scholar
  36. Daugirdas J, Kjellstrand C: Chronic hemodialysis prescription: a urea kinetic approach. Handbook of Dialysis. Edited by: Daugirdas J, Blake P, Ing T. 2001, Philadelphia: Lippincott Williams & Wilkins, 146-169.Google Scholar

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